Relationship between wintering latitude and arrival/departure timings of migratory birds
Karthik Thrikkadeeri
2024/08/15
Introduction
This notebook is the exploratory analysis notebook for the study. Here, I explore, mainly via visualisations, interesting patterns in arrival and departure times of some migratory bird species changing with their wintering latitudes.
Questions
Exploration
Investigating arrival and departure timings
After all our selection and filtering criteria for wintering species of interest, and after filtering data for each species to its wintering latitudinal range (removing latitudes where not purely wintering), we now start the analysis.
Using quantiles (assuming 95%), we determine “true” arrival and departure dates for each species per latitude. For a preliminary visualisation of patterns across species, we visualise this latitudinal trend of arrival (blue) & departure (red) times for all species:
We now calculate metrics for migration timings, such as first northern/southern arrival & departure, and synchronicity which is our primary metric of interest. We describe synchronicity using two (presumably) orthogonal angles: slope (quickness of migration) and tightness (uniformity) across latitudes. (Correlation R^2 cannot be used for the measure of tightness, since for high slope values, R2 becomes low.)
Here are the synchronicity measures (SYNC.SLOPE &
SYNC.TIGHT) for a set of illustrative species, followed by
updated plots for the same species.
## # A tibble: 50 × 6
## COMMON.NAME DATE.TYPE SLOPE SE SYNC.SLOPE SYNC.TIGHT
## <chr> <fct> <dbl> <dbl> <dbl> <dbl>
## 1 Cinereous Vulture DEP 6.21 0.921 -1.60 0.0827
## 2 Bar-tailed Godwit DEP 3.89 2.60 -1.19 -0.956
## 3 Brown-breasted Flycatcher DEP 2.47 0.479 -0.795 0.737
## 4 Black Redstart DEP 2.21 0.292 -0.696 1.23
## 5 Blyth's Reed Warbler DEP 1.86 0.213 -0.548 1.55
## 6 Red-breasted Flycatcher DEP 1.53 0.312 -0.373 1.16
## 7 Lesser Whitethroat DEP 1.50 0.462 -0.361 0.771
## 8 Common Chiffchaff DEP 1.46 0.410 -0.332 0.891
## 9 Siberian Stonechat DEP 1.39 0.246 -0.293 1.40
## 10 Bar-headed Goose DEP 1.26 0.283 -0.203 1.26
## 11 Taiga Flycatcher DEP 0.988 0.300 0.00665 1.21
## 12 Eurasian Wigeon DEP 0.795 0.344 0.197 1.07
## 13 Brown-headed Gull DEP -0.766 0.472 0.229 0.750
## 14 Brown Shrike DEP 0.519 0.282 0.570 1.27
## 15 Tufted Duck DEP 0.511 0.447 0.584 0.806
## 16 Spotted Redshank DEP 0.504 0.327 0.595 1.12
## 17 Greenish Warbler DEP -0.459 0.362 0.677 1.02
## 18 Gray Wagtail DEP 0.425 0.253 0.745 1.38
## 19 Green Warbler DEP 0.363 0.467 0.883 0.762
## 20 Common Buzzard DEP -0.272 0.880 1.13 0.128
## 21 Greater Spotted Eagle DEP 0.245 0.254 1.23 1.37
## 22 Sykes's Warbler DEP 0.147 0.847 1.67 0.166
## 23 Western Yellow Wagtail DEP 0.0612 0.241 2.44 1.42
## 24 Booted Eagle DEP -0.0444 0.250 2.72 1.39
## 25 Pallid Harrier DEP 0.0227 0.334 3.31 1.10
## 26 Blyth's Reed Warbler ARR -3.33 0.459 -1.06 0.778
## 27 Cinereous Vulture ARR -2.39 2.38 -0.766 -0.866
## 28 Green Warbler ARR -1.78 0.270 -0.510 1.31
## 29 Brown-breasted Flycatcher ARR -1.78 1.02 -0.506 -0.0229
## 30 Western Yellow Wagtail ARR -1.73 0.204 -0.481 1.59
## 31 Pallid Harrier ARR -1.62 0.240 -0.423 1.43
## 32 Sykes's Warbler ARR -1.51 0.984 -0.362 0.0157
## 33 Eurasian Wigeon ARR -1.35 0.272 -0.266 1.30
## 34 Common Chiffchaff ARR -1.22 0.440 -0.176 0.821
## 35 Brown-headed Gull ARR -1.04 0.533 -0.0368 0.630
## 36 Bar-tailed Godwit ARR -0.997 0.958 -0.000733 0.0428
## 37 Greenish Warbler ARR -0.980 0.280 0.0143 1.27
## 38 Booted Eagle ARR -0.976 0.209 0.0177 1.57
## 39 Brown Shrike ARR -0.732 0.160 0.270 1.83
## 40 Taiga Flycatcher ARR -0.722 0.250 0.281 1.39
## 41 Siberian Stonechat ARR -0.705 0.182 0.302 1.70
## 42 Tufted Duck ARR -0.700 0.527 0.308 0.640
## 43 Red-breasted Flycatcher ARR -0.642 0.248 0.384 1.39
## 44 Lesser Whitethroat ARR -0.610 0.255 0.429 1.36
## 45 Spotted Redshank ARR 0.552 1.02 0.516 -0.0168
## 46 Common Buzzard ARR 0.480 0.335 0.637 1.09
## 47 Black Redstart ARR -0.409 0.172 0.779 1.76
## 48 Gray Wagtail ARR 0.342 0.209 0.934 1.57
## 49 Bar-headed Goose ARR -0.129 0.146 1.79 1.92
## 50 Greater Spotted Eagle ARR 0.0515 0.332 2.59 1.10
All our species can be visualised as occupying a 2-D space governed by the two measures of synchronicity. Based on their occupancy of this space, we can classify their overall synchronicity.
Now will try to combine the two variables into a single index of synchronicity. Relative weights are obtained from PCA of the two variables, and the index is a linear combination of the two. New values and updated graphs below.
## # A tibble: 50 × 7
## COMMON.NAME DATE.TYPE SYNC.IND SLOPE SE SYNC.SLOPE SYNC.TIGHT
## <chr> <fct> <dbl> <dbl> <dbl> <dbl> <dbl>
## 1 Bar-tailed Godwit DEP -1.12 3.89 2.60 -1.19 -0.956
## 2 Cinereous Vulture DEP -1.08 6.21 0.921 -1.60 0.0827
## 3 Brown-breasted Flycat… DEP -0.320 2.47 0.479 -0.795 0.737
## 4 Black Redstart DEP -0.0982 2.21 0.292 -0.696 1.23
## 5 Lesser Whitethroat DEP -0.00962 1.50 0.462 -0.361 0.771
## 6 Common Chiffchaff DEP 0.0472 1.46 0.410 -0.332 0.891
## 7 Blyth's Reed Warbler DEP 0.102 1.86 0.213 -0.548 1.55
## 8 Red-breasted Flycatch… DEP 0.103 1.53 0.312 -0.373 1.16
## 9 Siberian Stonechat DEP 0.233 1.39 0.246 -0.293 1.40
## 10 Bar-headed Goose DEP 0.252 1.26 0.283 -0.203 1.26
## 11 Taiga Flycatcher DEP 0.378 0.988 0.300 0.00665 1.21
## 12 Brown-headed Gull DEP 0.391 -0.766 0.472 0.229 0.750
## 13 Eurasian Wigeon DEP 0.466 0.795 0.344 0.197 1.07
## 14 Tufted Duck DEP 0.653 0.511 0.447 0.584 0.806
## 15 Spotted Redshank DEP 0.757 0.504 0.327 0.595 1.12
## 16 Greenish Warbler DEP 0.782 -0.459 0.362 0.677 1.02
## 17 Brown Shrike DEP 0.786 0.519 0.282 0.570 1.27
## 18 Common Buzzard DEP 0.822 -0.272 0.880 1.13 0.128
## 19 Green Warbler DEP 0.846 0.363 0.467 0.883 0.762
## 20 Gray Wagtail DEP 0.940 0.425 0.253 0.745 1.38
## 21 Sykes's Warbler DEP 1.21 0.147 0.847 1.67 0.166
## 22 Greater Spotted Eagle DEP 1.27 0.245 0.254 1.23 1.37
## 23 Western Yellow Wagtail DEP 2.13 0.0612 0.241 2.44 1.42
## 24 Booted Eagle DEP 2.31 -0.0444 0.250 2.72 1.39
## 25 Pallid Harrier DEP 2.62 0.0227 0.334 3.31 1.10
## 26 Cinereous Vulture ARR -0.797 -2.39 2.38 -0.766 -0.866
## 27 Blyth's Reed Warbler ARR -0.487 -3.33 0.459 -1.06 0.778
## 28 Brown-breasted Flycat… ARR -0.357 -1.78 1.02 -0.506 -0.0229
## 29 Sykes's Warbler ARR -0.245 -1.51 0.984 -0.362 0.0157
## 30 Bar-tailed Godwit ARR 0.0127 -0.997 0.958 -0.000733 0.0428
## 31 Green Warbler ARR 0.0545 -1.78 0.270 -0.510 1.31
## 32 Common Chiffchaff ARR 0.133 -1.22 0.440 -0.176 0.821
## 33 Pallid Harrier ARR 0.151 -1.62 0.240 -0.423 1.43
## 34 Western Yellow Wagtail ARR 0.160 -1.73 0.204 -0.481 1.59
## 35 Brown-headed Gull ARR 0.170 -1.04 0.533 -0.0368 0.630
## 36 Eurasian Wigeon ARR 0.220 -1.35 0.272 -0.266 1.30
## 37 Spotted Redshank ARR 0.351 0.552 1.02 0.516 -0.0168
## 38 Greenish Warbler ARR 0.405 -0.980 0.280 0.0143 1.27
## 39 Tufted Duck ARR 0.411 -0.700 0.527 0.308 0.640
## 40 Booted Eagle ARR 0.498 -0.976 0.209 0.0177 1.57
## 41 Taiga Flycatcher ARR 0.624 -0.722 0.250 0.281 1.39
## 42 Red-breasted Flycatch… ARR 0.697 -0.642 0.248 0.384 1.39
## 43 Lesser Whitethroat ARR 0.719 -0.610 0.255 0.429 1.36
## 44 Siberian Stonechat ARR 0.736 -0.705 0.182 0.302 1.70
## 45 Brown Shrike ARR 0.754 -0.732 0.160 0.270 1.83
## 46 Common Buzzard ARR 0.779 0.480 0.335 0.637 1.09
## 47 Black Redstart ARR 1.08 -0.409 0.172 0.779 1.76
## 48 Gray Wagtail ARR 1.13 0.342 0.209 0.934 1.57
## 49 Bar-headed Goose ARR 1.83 -0.129 0.146 1.79 1.92
## 50 Greater Spotted Eagle ARR 2.13 0.0515 0.332 2.59 1.10## `geom_smooth()` using formula = 'y ~ x'
## `geom_smooth()` using formula = 'y ~ x'
There is still some finetuning to be done with the “quickness” metric, i.e., derived from slope. For the most synchronous species with little difference, the values change drastically. Also need to figure out how to appropriately weight the two so that high togetherness is prioritised.
Further try ordinations to understand what factors (wintering, migrating) determine synchronicity of species.